Sulfur is a co-product of oil and gas production that is produced in ever increasing quantities. For example, sulfur is currently produced at a rate of approximately 10,000 tons/day in Saudi Arabia. The rate of production is expected to increase to 12,000 tons/day in a few years. Although sulfur is a vital resource that is useful for the manufacture a myriad of products, the abundance of sulfur has resulted in worldwide reduction of its price. As worldwide sulfur supplies increase, the storage of the sulfur will present an environmental hazard. New uses of sulfur present one solution to the problem of storing the vast quantities of sulfur.
Previous studies relating to the degradation of PVAc in vacuum using TGA revealed a two stage decomposition. The first mass loss commenced at about 250° C. and continued to about 375° C., after which an inflexion preceded the second and final mass loss that ultimately led to complete decomposition of the polymer. The first mass loss stage was assigned mainly to the release of acetic acid and simultaneous formation of double bonds in the polymer backbone. The formation of both acetic acid and trans-vinylene species have been explained by comparison with pyrolytic cis or syn elimination of low molar mass ester model compounds. It was found that the addition of free radical inhibitors did not prevent elimination of acetic acid. However, previously studies also showed the formation of several volatile products using free radical mechanisms. It has also found that the acetic acid generated has a catalytic effect on degradation. This behavior has been compared to the catalytic effect of HCl on PVC.
Prior investigations have been conducted into inert and oxidative thermal degradation mechanism of PVAc and EVA copolymers using semi-crystalline and amorphous EVA having a VA content in the polymer backbone ranging from about 9 to 73% by weight. More specifically, EVA emulsions of Airflex EN 1035 and Airflex BAF 60 (55 and 60% solids in water, respectively) from Air Products containing 73 and 60% by weight vinyl acetate were utilized. The thermal study was performed over a temperature range of about 200° C. (to remove water and monomers) to about 600° C. and 650° C. for inert and oxidative conditions respectively. The inert degradation of PVAc as measured using a TGA coupled with mass spectrometry (TGA-MS) showed two degradation steps: the first and most intense step is deacytelation, which occurs between about 300 and 400° C. The end of the first thermal degradation step of PVAc in air has been reported to be around 310° C., corresponding to a loss of 95% of the acetic acid formed in the degradation process. Studies have shown that the major volatile degradation product is acetic acid, with smaller amounts of ketene, water, methane, carbon dioxide and carbon monoxide also being formed. Analysis of the degraded sample at 400° C. shows a highly regular unsaturated material. The second step of degradation involves a dehydrogenation reaction.
Thus, there exists a need to provide a modified polymer having improved properties, such as increased melting point, while at the same time providing a use for excess sulfur. One application for such a modified polymer is a sulfur modified polymer for use in asphalt compositions.